This invention relates to torsional vibration dampers such as twin mass flywheels and in particular such flywheels used to connect an internal combustion engine with a gearbox on a motor vehicle.
In, for example, earlier granted patents GB 2229793 and 2282868 and pending applications PCT/GB95/01976 and PCT/GB97/00361 there are described torsional vibration dampers in the form of twin mass flywheels in which an input element and an output element are relatively rotatable against the action of a damping means which includes a plurality of linkages each linkage including one or more link members which act as bob-weights to provide a speed dependant damping on the relative rotation of the flywheel elements. The earlier patent applications GB-A-2220464 and PCT/GB97/00362 also disclose torsional vibration dampers used in combination with a fluid coupling in which the relative rotation of input and output elements of the damper is again controlled by a plurality or such linkages.
In the earlier UK application no. 98 01329.5 a number of twin mass flywheel constructions are proposed for overcoming the effect of the tilting of the input flywheel element out of its nominal plane of rotation due to flexing of the crank shaft of the associated internal combustion engine. These various earlier proposals allow relative tilting of the input and output flywheel elements to be accommodated via various self-aligning bearing arrangements which either constitute the main bearing support between the flywheel elements or bearings associated with the bob-weight or other link pivots of the linkages.
It is an object of the present invention to provide further constructions for ameliorating the effect of the tilting of the input element of such a flywheel or the input element of a torsional vibration damper of the form described in GB-A-2220464 and PCT/GB97/00362 referred to above which can be used either in addition to or instead of the various constructions disclosed in the previously referred to UK application no. GB 9801329.5.
Thus according to the present invention there is provided a torsional vibration damper comprising an input element and an output element which are relatively rotatable against the action of a damping means which includes a plurality of linkages, each linkage comprising plurality of interconnected links, the damper being characterized in that at least one of the links is flexible in an axial sense relative to the remainder of the damper to accommodate forces applied to the flexible link as a result of relative tilting of the damper elements.
The present invention is equally applicable to a torsional damper in the form of a twin mass flywheel where the input and output elements comprises input and output flywheel masses respectively or to a damper in which the input and output elements are of relatively light mass and are connected in a drive-line, for example in combination with a fluid coupling as discussed above.
Each linkage may include one or more generally radially extending links pivoted on one element, the or each radially extending link being interconnected with the other element via one or more additional links.
The generally radially extending links and/or the additional links may flex to accommodate relative fitting of the elements.
The generally radially extending links may be arranged to flex by forming an intermediate portion thereof of a smaller axial dimension than the end portions of said link. Typically such a link will be manufactured from an alloy steel to accommodate flexing.
Alternatively, the generally radially extending links may each be formed with an intermediate portion formed from spring steel which is secured to end portions which contain the pivotal connections with the damper element and additional link respectively.
The end portions of each generally radially extending link may be arranged to contact each other after a given amount of axial flexing to limit the maximum axial flexing.
The generally radially extending links may have a concentration of mass at their radially outer ends thus operating as bob-weights which damp the relative rotation of the damper elements.
Each additional link may comprise one or more parallel flexible arms.
For example, each additional Ink may comprise a single flexible arm, the arm being off-set in an axial sense to one side of the associated generally radially extending link.
In an alternative construction each additional link may comprise a single flexible arm mounted centrally in an axial sense relative to the associated generally radially extending link.
In a still further alternative each additional link may comprise a pair of parallel axially spaced flexible arms located one on each side in an axial sense of the associated generally radially extending link.
The additional links may have a mass concentration therein located at the ends of the additional links which are connected with the generally radially extending links.
In addition to use in a vibration damper in which each linkage comprises only two links the present invention is also applicable to dampers which use multi-link linkages to connect the input and output damper elements as, for example, in the Applicant""s earlier patent application No PCT/GB97/00361.
The invention also provides a torsional vibration damper comprising relatively rotatable input and output elements which are interconnected by a plurality of linkages which each includes one or more generally radially extending links and one or more generally circumferentially extending links, the damper being characterized in that the generally circumferentially extending links have a mass concentration adjacent one end thereof connected with the generally radially extending links.